Japanese Patent Laid-Open No. 11-41523 discloses a technique for making an image sensing operation using a focal plane shutter (to be referred to as a mechanical shutter hereinafter) and an electronic shutter together in a single-lens reflex type digital camera. In a shutter mechanism of this type, the mechanical shutter forms a rear curtain, and an image is captured by driving the electronic shutter that performs a charge accumulation start scan of pixels of an image sensing element prior to traveling of the rear curtain. In an image sensing element using a CMOS sensor, resetting of pixels (to scan to set accumulated charge amounts of pixels to zero) is done for each pixel or for each region including a plurality of pixels. After an elapse of a predetermined period of time for each pixel or region, a signal read scan is made to implement the electronic shutter. That is, in the charge accumulation start scan of the image sensing element, pixels are reset for, e.g., each scan line, and charge accumulation starts. Such charge accumulation start scan will be referred to as a reset scan hereinafter. After the image sensing element is shielded by the mechanical shutter as the rear curtain, a read scan for reading out charges accumulated on elements of respective pixels is made. Therefore, the scan pattern of this reset scan corresponds to the traveling characteristics of the mechanical shutter as the rear curtain.
In recent years, single-lens reflex type digital cameras have prevailed. The single-lens reflex type digital cameras can normally exchange photographing lenses, and the focal length and the exit pupil distance (the distance from an image sensing plane to the exit pupil position of the lens) changes depending on the photographing lenses attached. When the image sensing apparatus is configured using the aforementioned shutter mechanism that uses the mechanical shutter and electronic shutter together, the electronic shutter functions on the image sensing element surface, but the mechanical shutter is set to be separated from the image sensing element surface in the optical axis direction. Therefore, the light-shielding position of the image sensing plane by the mechanical shutter changes depending on the focal lengths, exit pupil distances, and the like of the photographing lenses. For this reason, when a time period from execution of the reset scan to light-shielding by the mechanical shutter is short, exposure nonuniformity occurs in the shutter traveling direction depending on the mounted photographing lenses.
Also, in some cameras, the exit pupil distance changes depending on stopping-down of a photographing lens, the focus position of a macro lens, and the like. Furthermore, when an anti-vibration lens is mounted, the light-shielding position of the mechanical shutter changes depending on the shift amount of that lens. Therefore, due to these factors, the aforementioned exposure nonuniformity in the shutter scan direction occurs.
To solve these problems, in the shutter mechanism that uses the mechanical shutter and electronic shutter together, further improvements to eliminate exposure nonuniformity in the shutter scan direction due to the circumstances of the lenses or image sensing elements are needed.